There is known a gas sensor of the type mounted on an exhaust pipe of an automotive vehicle so as to detect the concentration of oxygen in exhaust gas. This gas sensor includes a gas sensor element having a bottomed cylindrical base body formed of a solid electrolyte with a closed front end and an open rear end and extending in an axial direction of the gas sensor, an outer electrode formed of noble metal (such as platinum) on an outer surface of the base body and an inner electrode formed of noble metal (such as platinum) on an inner surface of the base body (see, for example, Patent Document 1).